(1) Field of the Invention
The present invention relates to a code division multiple access communicating system, a base station for a code division multiple access communicating system and a terminal apparatus for a code division multiple access communicating system, and a code division multiple access communicating method, suitable for a communication of spread spectrum information with a base station over a commonly used channel.
(2) Description of Related Art
With an increase of demand for portable telephones, efficient use of a frequency becomes a serious problem in a mobile communication system. In such circumstances, a code division multiple access (CDMA) communicating system using a spread spectrum technique draws attention as a system having a high frequency efficiency, searches on it being vital for the purpose of practical application thereof.
In a CDMA communicating system, the user uses a mobile station (hereinafter referred to as MS) to transmit a frame to a base station (hereinafter referred to as BS) at a transmittable timing according to notice information transmitted from the BS when making a telephone call, for example.
A frame transmitted from a portable telephone to a BS is transmitted at a timing in a predetermined cycle, as shown by a plurality of arrows in FIG. 24(b). In FIG. 24(b), there are, for example, four timings that the portable telephone can access to the BS in one cycle. Each portable telephone randomly selects any one of the timings to transmit a frame to the BS.
FIG. 24(b) shows that MSs 1a through 4a transmit frames to the BS at different timings. Incidentally, frames transmitted from the MSs 1a through 4a are spread using a spreading code and transmitted to the BS. The MSs 1a through 4a transmit frames at different timings, so that a timing of a phase of the spreading code shifts with a transmit timing even if the spreading code used by MSs 1a through 4a has the same system. The BS can thereby de-spread each of the frames transmitted from the MSs 1a through 4a on the basis of the spreading code having a phase different from one another so as to extract the frame.
When the BS receives frames transmitted from the MSs 1a through 4a, the BS transmits ACKs (Acknowledge) as acknowledge information to the MSs 1a through 4a (transmitting side), as shown in FIG. 24(a). In ACKs, plural pieces of acknowledge information for the MS 1a through 4a are collected in a transmission frame, and transmitted.
Each of the MSs 1a through 4a receives a frame outputted from the BS after transmitting the frame to confirm whether or not the frame having been transmitted to the BS is received by the BS. When there is acknowledge information to the frame having been transmitted from itself in the received frame, each of the MSs 1a through 4a confirms reception of the frame having been transmitted to the BS by the BS. When each of the MSs 1a through 4a does not receive acknowledge information to the frame having been transmitted from itself within a predetermined period after transmitting the frame to the BS, the MS performs a re-transmitting process. When receiving ACK to the information having been transmitted from itself within a predetermined period after transmitting the frame to the BS, each of the MSs 1a through 4a transmits a remaining frame when having the remaining frame to be continuously transmitted to the BS.
When transmitting a plurality of frames to the BS, each of the MSs 1a through 4a recevies ACK each time the MS transmits a frame, then transmits a remaining frame.
In the case where each of the MSs 1a through 4a transmits one frame, receives ACK shown in FIG. 24(a), and the MS 1a and MS 2a transmit remaining packets as shown in FIG. 24(b), each of the MS 1a and the MS 2a possibly access to the BS at the same timing since each of the MS 1a and the MS 2a can randomly select an access timing among four access timings in one frame.
At this time, information transmitted from the MS 1a and the MS 2a is spread using the spreading code having the same phase, so that the BS cannot separate the information transmitted from the MS 1a and the MS 2a, hence the information is lost. The MS 1a and the MS 2a therefore cannot receive acknowledge information to the frames that the MS 1a and the MS 2a have secondary transmitted to the BS, thus the MSs 1a and 2a have to perform the re-transmitting process. This leads to a decrease of a throughput of the communicating system.
In the light of the above disadvantage, an object of the present invention is to provide a code division multiple access communicating system, a base station for a code division multiple access communicating system and a terminal apparatus for a code division multiple access communicating system, and a code division multiple access communicating method, in which when a terminal apparatus continuously transmits remaining information after receiving acknowledge information from a base station, the terminal apparatus again accesses to the base station according to an order of a piece of acknowledge information for itself among plural pieces of acknowledge information having been put in a transmission frame, whereby conflict of access timings between terminal apparatus whose acknowledge information has been put in the transmission frame is avoided, thus a decrease of the throughput can be suppressed.
A code division multiple access communicating system according to this invention comprises a base station and a plurality of terminal apparatus exchanging spread spectrum information with the base station over a commonly used channel when communicating with the base station.
The base station comprises a receiving means for receiving an access signal from each of the plural terminal apparatus at the time of random access from each of the plural terminal apparatus, and an acknowledge information transmitting means for collectively putting plural pieces of acknowledge information to reception of the access signals for the plural terminal apparatus in a transmission frame, and transmitting the frame to the plural terminal apparatus when receiving means receives the access signals from the plural terminal apparatus.
Each of the plural terminal apparatus comprises an acknowledge information receiving means for receiving the plural pieces of acknowledge information from the acknowledge information transmitting means of the base station, and a transmitting means for again accessing to the base station according to an order of acknowledge information for its own terminal apparatus among the plural pieces of acknowledge information received from the base station by the acknowledge information receiving means was put after randomly accessing to the base station when there is remaining information to be continuously transmitted to the base station, and transmitting the remaining information.
In the code division multiple access communicating system of this invention, the terminal apparatus again accesses to the base station according to an order of acknowledge information for itself among plural pieces of acknowledge information received from the base station by the acknowledge information receiving means to transmit remaining information, whereby conflict between the terminal apparatus transmitting remaining information is avoided and a decrease of the throughput is suppressed.
A base station for a code division multiple access communicating system of this invention comprises a receiving means for receiving an access signal from each of a plurality of terminal apparatus at the time of random access from each of the plural terminal apparatus, and an acknowledge information transmitting means for collectively putting plural pieces of acknowledge information to reception of the access signals for the plural terminal apparatus in a transmission frame in the order the access signals were received from the plural terminal apparatus when receiving the access signals from the plural terminal apparatus by the receiving means, and transmitting the transmission frame to the plural terminal apparatus so that the plural terminal apparatus having remaining information to be continuously transmitted to the base station again access to the base station in a predetermined order to transmit the remaining information.
Accordingly, the base station for a code division multiple access communicating system of this invention collectively puts plural pieces of acknowledge information for a plurality of terminal apparatus in a transmission frame in the order the base station received access signals from the plural terminal apparatus and transmits the transmission frame to the plural terminal apparatus so that the plural terminal apparatus having remaining information to be continuously transmitted to the base station again accesses to the base station in a predetermined order, whereby conflict between terminal apparatus transmitting remaining information is avoided, and a decrease of the throughput is thus suppressed.
A terminal apparatus for a code division multiple access communicating system of this invention comprises a randomly accessing means for randomly accessing to a base station, an acknowledge information receiving means for receiving plural pieces of acknowledge information from the base station, the base station collectively putting acknowledge information for the terminal apparatus along with acknowledge information for other terminal apparatus in a transmission frame, and transmitting the transmission frame to the terminal apparatus when receiving an access signal from the terminal apparatus at the time of random access by the terminal apparatus to the base station, and a transmitting means for again accessing to the base station according to an order of the order acknowledge information for the terminal apparatus of its own among the plural pieces of acknowledge information received from the base station by the acknowledge information receiving means after the terminal apparatus randomly accesses to the base station if there is remaining information to be continuously transmitted to the base station, and transmitting the remaining information.
Accordingly, in the terminal apparatus for a code division multiple access communicating system of this invention, the transmitting means again accesses to the base station according to an order of acknowledge information for a terminal apparatus of its own among plural pieces of acknowledge information received from the base station by the acknowledge information receiving means after randomly accessing to the base station, whereby conflict between terminal apparatus transmitting remaining information, and a decrease of the throughput is thus suppressed.
A code division multiple access communicating method of this invention comprises the steps of an acknowledge information transmitting step performed in a base station of collectively putting acknowledge information for a plurality of terminal apparatus in a transmission frame when the base station receives access signals from the plural terminal apparatus at the time of random access from the plural terminal apparatus, and transmitting the transmission frame to the plural terminal apparatus, and a transmitting step performed in each of the plural terminal apparatus of again accessing to the base station according to an order of acknowledge information for itself among the plural pieces of acknowledge information received from the base station in the transmission frame after a random access to the base station if there is remaining information to be continuously transmitted to the base station to transmit the remaining information.
According to the code division multiple access communicating method of this invention, each of a plurality of the terminal apparatus again accesses to the base station according to an order of acknowledge information for itself among plural pieces of acknowledge information received from the base station if having remaining information to be continuously transmitted to the base station after randomly accessing to the base station to transmit the remaining information at the transmitting step, whereby conflict between terminal apparatus transmitting remaining information is avoided, and a decrease of the throughput is thus suppressed.